1. Field of the Invention
The present invention relates in general to a fluid-filled cylindrical elastic mount, and in particular to such an elastic mount which has a pressure-receiving chamber and an equilibrium chamber each filled with a suitable non-compressible fluid, and damps vibrations based on fluid resistance to flows of the fluid between the two chambers.
2. Discussion of the Prior Art
There is known a cylindrical elastic mount which is used as a vibration-damping mounting device or connecting device such as an engine mount and a suspension bushing for automotive vehicles. The cylindrical elastic mount includes an inner and an outer sleeve which are disposed concentric or eccentric with each other, and an elastic member of rubber interposed between the two sleeves for flexible connection therebetween.
Recently, there has been used a "fluid-filled" cylindrical elastic mount which has a plurality of pockets formed in the elastic member thereof and opening in an outer circumferential surface of the elastic member, and at least one metallic sleeve disposed over at least the outer circumferential surface of opposite axial end portions of the elastic member. In this elastic mount, the outer sleeve is fitted on the outer circumferential surface of the elastic member via the at least one metallic sleeve and a rubber sleeve for fluid-tight sealing between the metallic sleeve and the outer sleeve. The plurality of pockets are filled with a suitable non-compressible fluid so as to provide a plurality of fluid chambers in the elastic mount. The plurality of fluid chambers are held in fluid communication with each other through a restricted passage, i.e., an orifice. Upon application of vibrations to the elastic mount, the orifice exhibits a resistance to the fluid flowing therethrough, or the fluid existing in the orifice resonates, thereby damping the vibrations.
An example of the fluid-filled cylindrical elastic mount of the above-described type is disclosed by U.S. Pat. No. 4,749,173 (published on June 7, 1988). The disclosed elastic mount has a plurality of fluid chambers, one of which serves as a pressure-receiving chamber whose fluid pressure is changed, upon application of vibrations to the bushing, due to relative displacement of the inner and outer sleeves thereof. The plurality of fluid chambers also include at least one volume-variable equilibrium chamber which is at least partially defined by a flexible diaphragm and whose change in fluid pressure is accommodated by elastic deformation of the flexible diaphragm. Upon input of vibrations to the elastic mount, the fluid flows between the pressure-receiving and equilibrium chambers via a restricted passage or an orifice due to pressure change produced in the pressure-receiving chamber, so as to damp the vibrations.
In the above fluid-filled elastic mount, the elastic member has an axial recess formed through a portion thereof which portion is subjected to tensile stress due to a static load upon installation thereon of a load member to be supported thereby, namely, upon application thereto of the weight of a load member. The axial recess contributes to minimizing the tensile stress produced in the portion in question of the elastic member. Thus, the durability of the elastic member is improved.
However, the above-indicated prior art elastic mount suffers from a problem that the flexible diaphragm associated with the equilibrium chamber is excessively largely expanded or elastically deformed due to an excessive amount of fluid flowing from the pressure-receiving chamber into the equilibrium chamber through the orifice as a result of an extremely increased fluid pressure in the pressure-receiving chamber upon application of a large vibrational load to the mount. Consequently the flexible diaphragm tends to be deteriorated. The deteriorated diaphragm may not accommodate a largely increased volume of the equilibrium chamber and in such a case may break. Thus, the durability and reliability of the flexible diaphragm, and accordingly those of the elastic mount itself, have been unsatisfactory.